Loud speaking telephone system



H. A. HowELL LOU SPEAKING TELEPHONE SYSTEM Nov. 16, 1937.

Filed Aug. 19. 1956 R. Y. m m. um EW n WI A O A w H Patented Nov. 16, 1937 UNITED s'rATEs PATENT OFFICE 2,0 9a44z LoUn srEAKING TELEPHONE SYSTEM tion of Illinois Application August 19, 1936, Serial No. 96,762

2 Claims.

This invention relates to an improved loud speaking telephone system and relates particularly to an intercommunicating system which can be used to carry on a conversation between two 5 or more points in somewhat the same manner as the party-line telephone system.

Another important object of the invention is to provide an intercommunicating system which employs only one amplifier unit for a plurality of stations up to the capacity limit.

Another important object is the provislon of a specially balanced in-put circuit in the amplifier in order to prevent feed back or howling.

Another and still further important object of the invention is the automatic elimination of the undesirable pick-up of hum or other interference due to floating or loose-end input wires or to station units which might be normally in the receiving condition but beyond the particular stations 'o in use at a certain time.

Other and further important objects of the invention will be apparent from the disclosures in the accompanying drawing and following specification.

u The invention, in a preferred form, is shown in the drawing and hereinafter more fully described.

In the drawing:

Figure 1 illustrates a complete lay-out of the 'o loud speaking telephone system of this invention,

illustrating three stations and indicating connections for more.

As shown in the drawing: VThe reference numeral |0 indicates generally 5 the loud-speaker of what is known as the near end station of the intercommunicating system of this invention, and it will be noted that there are similar loud-Speakers l2 and ll at the intermediateand end stations respectively.

o Connections IS are provided at the end station which can be used to hook up one or more stations, the last of which then, of course, would be the end station, making the station |4 an intermediate station. w

5 The arrangement of each of the stations is the same with the exception that the near-end station is provided with a. ground connection |8, and

it will further be noted that the loud-speaker is usedforrboth receiving and 'transmitting Each of the stations is provided with a pushbutton or switch which is of such a type that,

when the switch is depressed, 'the circuit 22, which is normally connected, is opened, and 'a connection is made'at the same time to a wire 24 which, in the case of the intermediate stations,

runs to the end station, and, in the case of the end station, is connected to a special input transformer 26.

At the same time that the connection is made with the wire 24, another connection with the Wire 28 is broken, this being for the purpose of automatically cutting out stations beyond thel one which is in use, thereby eliminating the pick-up of hum or other interference due to fioating or loose-end input wires to station units which 10 would normally be in the receiving condition. When the push-button of any station unit is depressed to talk position as hereinabove described,

' the input Wire to all station units not located between the talking station and the amplifier -is 15 automatically disconnected. For example, in the system shown in the drawing, the far-end station which employs the combination speaker and receiver M is disconnected when the'intermediate station is in talk position. Likewise, when the station nearest the amplifier is in 4the talk condition, both the intermediate and far-end station input leads-are disconnected at both ends.

The amplifier is shown at 28 and consists of ,the usual arrangement, and is provided with an output transformer 40.

In order to use one amplifier unit for two or more station units, a special balanced input circuit has been incorporated into the amplifier unit in order to prevent feed back or howling due to the capacity coupling and` cross-talk between the inputand output wires in the two-Wire cable. It will be noted that ,this cable includesa shield 30.

Whenever the line in the system of this invention is over a certain minimum, approximately 5 fifty feet, a small amount of the output of the amplifier 28 is fed back to the input due to coupling between the input and output wires in the cable notwithstanding the presence of the shield 30. This usually sets up a high frequency squeal, and in order to eliminate this, a small amount of the output is fed through a small variable capacity which includes a balanced condenser 32 and a special extra primary winding 34 of the coil 26 of the input transformer. The 45 direction of this special winding is opposite to the regular primary winding so as to produce the desired effect. When the system is set up, the condenser 32 is adjusted ,to offset the capacity due to the coupling of the line, and, lthereupon, the energy fed to the special winding 34 of the primary will balance out the energy due to capacity coupling in the second primary of the coil 26. In this manner, squeal or other undes'irable noises are efiectively-prevented, and inasmuch added.

It will be' evident that herein is presented an i economieal intercommunicating system which is so designed that as many as four station units may be operated on one amplifier unit and which can be readily set up and installed with no special tools or equipment whatsoever.

The simplifled arrangement, which includes the quick action push-button, enables immediate lchange from receiving to talking position in any unit, and when party is talking, all other stations in the circuit will be responsive as all sta- Itions remain in the receiving condition so long as the talking button is not operated.

The device can be used as a two-way loud speaking telephone between any two points up to as far as five hundred feet apart, such as, for example, from a house to a garage, from a basement ,to an attic or any other point in a house, or even between two o r three houses. Other uses are as an intercommunicating system in offices and shops or between shops and ofiices, and the device is so simple and economically constructed that it can even be marketed as an amusement device or a toy for children which will possess the additional advantage of being highly instructive and educational.

I am aware that many changes may be made as this is accomplished when the system is Set and numerous detailsv of construction varied ,throughout a wide range without departing from the principles of this invention, and I, therefore, do not purpose limiting the patent granted hereon otherwise than as necessitated by the prior art.

I claim as my invention:

1. An intercommunicating system, comprising a plurality of combined receiving and transmitting units, and a single amplifier for all the units, together with a special input transformer associated with the amplifier, the special input transformer including a double primary winding, together with a balanced input circuit in the amplifier unit, said input circuit including a variable' condenser and switch means for retaining .all the units in receiving position.

2. An intercommunicating system, comprising a plurality of combined receiving and transmitting units, and a single amplifier for all the units, together with switch means for retaining all'the units in receiving position, and means for automatically cutting out units beyond a particular unit when the switch is depressed to talking position and when more than two parties are connected in the system, together with means for preventing feed-back when using a high impedance line, said means including a three-winding input transformer and a small capacitor.

HUGH A. HOWELL. 

